KCNA said Mr Kim was speaking at a military exercise on Thursday, which is thought to be when the projectiles were fired.

He said North Korea "must always be ready to fire our nuclear warheads at any time" because enemies were threatening the North's survival.

"At an extreme time when the Americans... are urging war and disaster on other countries and people, the only way to defend our sovereignty and right to live is to bolster our nuclear capability," he was quoted as saying.

Image copyrightAPImage caption
Footage of North Korea launching short-range projectiles into the sea was shown on South Korean TV

Analysts still doubt whether North Korea has the ability to make a nuclear bomb small enough to put on a feasible missile, but Kim Jong-un's announcement brought a swift response from the US.

"We urge North Korea to refrain from provocative actions that aggravate tensions and instead focus on fulfilling its international obligations and commitments," Pentagon spokesman Commander Bill Urban said.

The US and South Korea began talks on Friday on the possible deployment of a US missile defence shield in the South.

Initial talks will focus on the costs, effectiveness and environmental impact of installing the Terminal High Altitude Area Defense (THAAD) system, among other issues, the Yonhap news agency reported.

What is the Terminal High Altitude Area Defense System (Thaad)?

Shoots down short and medium-range ballistic missiles in the terminal phase of their flight